Abstract
AbstractThe effect of gamma irradiation dose on microscopic structure of polymethylmethacrylate (PMMA) has been studied using positron annihilation lifetime (PAL) and Doppler broadening of annihilation radiation (DBAR) techniques. The measurements were performed at room temperature as a function of the γ‐irradiation doses from 60‐1200 kGy. The observed lifetime spectra were resolved into three components. The size and the fraction of the o‐Ps hole volume were estimated from the positron annihilation parameters. The effect of γ‐irradiation was identified at lower doses to be cross‐linking while at higher doses the chemical degradation of the polymer was observed. Moreover, the distribution of the free volume shifts from a large to small size as the irradiation increases and has very similar Gaussian‐like distribution. The PAL results were confirmed with X‐ray measurement. A correlation between the macroscopic mechanical properties Hv and positron annihilation parameters has been demonstrated. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
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